The introduction of an endotracheal tube (ETT) into the trachea is a common medical procedure performed during resuscitation and anaesthesia. It is referred to as “intubation” and is intended to provide a secure airway in patients who are unable to manage their breathing. Greater than 4.5 million intubations occur worldwide per year.
This is usually performed under direct vision using a laryngoscope. Laryngoscopes come in a variety of patterns but essentially comprise a light source, a blade and a handle. Using the blade as a spatula the laryngoscope is inserted through the mouth behind the base of the tongue and is then placed above the larynx in order to visualise the vocal cords (chords). Once the laryngoscope is in place an endotracheal tube is guided manually under direct vision between the chords and into the upper trachea. Recently a number of video laryngoscopes have become available, these devices are designed to provide a clearer view of the vocal chords and surrounding structures by virtue of a camera being placed close to the tip of the blade. The image from this camera is typically displayed on a screen attached to the handle of the video-laryngoscope, or placed remotely, but within visual range of the operator.
There are a number of situations that can make intubation difficult and in some cases impossible. These include an inability to sufficiently open the mouth due to trauma, inability to flex or extend the neck due to trauma or pathology in the cervical spine or distortion of the anatomy surrounding the glottis due to tumours, haemorrhage, etc. The inability to intubate a patient can constitute a medical emergency and in some cases can result in death. A number of techniques have been developed to help clinicians overcome some of these difficult situations.
One technique is the use of a guide or a bougie to negotiate a pathway between the vocal chords. Once a bougie is successfully in place an endotracheal tube can be placed over the bougie and slid down to follow the bougie through the chords, this technique is commonly referred to as “railroading”.
The advantage of placing the bougie through the chords is that it is of a significantly smaller diameter (typically 4-5 mm) in comparison to the ETT which can range from 5-12 mm. This allows much greater visibility when guiding the bougie through the chords. With both conventional and video laryngoscopes a large diameter ETT can obscure vision of the chords. The ETT is normally moulded with a curve that allows it to follow the curved pathway from the oral opening to the chords. However, in many cases the angle at which the tip of the ETT presents itself to the opening between the chords does not allow the ETT tube to negotiate this space. Furthermore, the bougie can be made from relatively stiff material which is easier to control in terms of guiding it through the chords. Additionally, the end of the bougie may be formed with an angled tip, which provides the capacity to manoeuvre the tip through the chords by rotating the bougie so the tip can be positioned optimally to advance.
A number of bougies are currently available for this purpose and are designed using different materials, diameters and tip angles.
There are, however, occasions where the tip angle is insufficient or too great to position these bougies within the chords.
Additionally, in some circumstance it is helpful to be able to introduce oxygen into the patient's airway during the intubation process. Therefore some bougies have an internal passageway to channel oxygen from the proximal end to the distal end of the bougie, that is they are hollow. When additional oxygen is used in this way, it may be introduced in a manner that assists in ventilation. This can occur by the entrainment of air into the trachea, a technique known as jet ventilation or the agitation of surrounding air this technique is known as high frequency jet ventilation.